Raman spectroscopy has numerous applications in the field of biology. One such application is the simultaneously measurement of the concentration of multiple biochemical components in low volume aqueous mixtures, for example, a single drop of blood serum. Over twenty years ago, it was shown for the first time that it was possible to estimate the concentration of glucose, urea, and lactic acid in mixture by combining Raman Spectroscopy with Partial Least Squares Regression analysis. This was followed by numerous contributions in the literature designed to increase the number of components and reduce the limits of concentration that could be simultaneously measured using Raman spectroscopy, by developing various optical architectures to maximise the signal to noise ratio. The aim of this paper is to demonstrate the potential of a confocal Raman microscopy system for multicomponent analysis for the case of physiologically relevant mixtures of glucose, urea, and lactic acid.
Raman spectroscopy is a powerful tool for analyzing the composition of biological samples in terms of biomolecular content. Over the past two decades there has been considerable interest in the application of Raman to measuring the concentration of the various constituents in a multicomponent mixture. This is achieved by first building a database of the Raman spectra of the individual components in a pure form. Following this a least squares algorithms is applied to find a best fit that accounts for the spectrum of the mixture. The weights returned by a partial least squares algorithm indicate the relative concentration of each component. Of particular interest has been application of the method to estimate the concentration of various analytes in blood and urine samples, including glucose. In this paper we briefly review the subject of multicomponent analysis by Raman Spectroscopy in terms of experimental methodology, limits of measurement, and applications
Studies of neurovascular coupling (hemodynamic changes and neuronal activation) in the visual cortex using a time-domain single photon counting system have been undertaken. The system operates in near infrared (NIR) range of spectrum and allows functional brain monitoring to be done non-invasively. The detection system employs a photomultiplier and multi-channel scaler to detect and record emerging photons with sub-microsecond resolution (the effective collection time per curve point is ~ 200 ns). Localisation of the visual evoked potentials in the brain was done using knowledge obtained from electroencephalographic (EEG) studies and previous frequency-domain optical NIR spectroscopic systems. The well-known approach of visual stimulation of the human brain, which consists of an alternating black and white checkerboard pattern used previously for the EEG study of neural responses, is applied here. The checkerboard pattern is synchronized with the multi-channel scaler system and allows the analysis of time variation in back-scattered light, at different stimulation frequencies. Slow hemodynamic changes in the human brain due to Hb-HbO<sub>2</sub> changes in the blood flow were observed, which is evidence of the system's capability to monitor these changes. Monocular visual tests were undertaken and compared with those done with an EEG system. In some subjects a fast optical response on a time scale commensurate with the neural activity associated with the visual cortex was detected. Future work will concentrate on improved experimental protocols and apparatus to confirm the existence of this important physiological signal.
In this work a mechanical optode mounting system for functional brain imaging with light is presented. The particular application here is a non-invasive optical brain computer interface (BCI) working in the near-infrared range. A BCI is a device that allows a user to interact with their environment through thought processes alone. Their most common use is as a communication aid for the severely disabled. We have recently pioneered the use of optical techniques for such BCI systems rather than the usual electrical modality. Our optical BCI detects characteristic changes in the cerebral haemodynamic responses that occur during motor imagery tasks. On detection of features of the optical response, resulting from localised haemodynamic changes, the BCI translates such responses and provides visual feedback to the user. While signal processing has a large part to play in terms of optimising performance we have found that it is the mechanical mounting of the optical sources and detectors (optodes) that has the greatest bearing on the performance of the system and indeed presents many interesting and novel challenges with regard to sensor placement, depth of penetration, signal intensity, artifact reduction and robustness of measurement. Here a solution is presented that accommodates the range of experimental parameters required for the application as well as meeting many of the challenges outlined above. This is the first time that a concerted study on optode mounting systems for optical BCIs has been attempted and it is hoped this paper may stimulate further research in this area.
In this work an image-based photoplethysmography (PPG) system is developed and tested against a conventional finger-based system as commonly used in clinical practise. A PPG is essentially an optical instrument consisting of a near infrared (NIR) source and detector that is capable of tracking blood flow changes in body tissue. When used with a number of wavelengths in the NIR band blood oxygenation changes as well as other blood chemical signatures can be ascertained yielding a very useful device in the clinical realm. Conventionally such a device requires direct contact with the tissue under investigation which eliminates the possibility of its use for applications like wound management where the tissue oxygenation measurement could be extremely useful. To circumnavigate this shortcoming we have developed a CMOS camera-based system, which can successfully extract the PPG signal without contact with the tissue under investigation. A comparison of our results with conventional techniques has yielded excellent results.
This study investigates the feasibility of acquiring fast optical response signals from the peripheral nervous system (PNS) and specifically to obtain knowledge about the sensory response of the median nerve through comparing electrophysiological responses with those obtained with a single photon counting system. Nerve potentials have been well studied so the primary purpose of this investigation is to better understand the conditions required for recording the optical analogue of this signal. Such action potential-correlated optical signals have been termed 'fast optical evoked responses' and their measurement in-vivo has hitherto proved fraught with difficulty. As yet measurement of these signals has been confined to evoked potential studies in the brain and so far there is no repeatable, confirmed procedure for their robust acquisition. In this work it is suggested that perhaps an easier route to acquire these elusive optical signals is through evoked potential studies centred on the PNS as opposed to the brain. Preliminary results suggest it is possible to correlate both data and draw important information from it although the most important contribution of this paper is the principle of directing the search for robust fast optical signals to the peripheral nervous system as opposed to the brain.